To better understand the principle of the invention, it would be advantageous to define in a simple way some terminology that relates to the field of treatment of cerebral artery diseases.
Arterial Supply: Blood is supplied to the brain by three major artery systems: the right and left internal carotid arteries and the vertebral/basilar system. The carotid arteries supply the anterior two-thirds of the cerebral hemispheres, and the vertebral/basilar system supplies the brainstem and cerebellum and posterior parts of the hemispheres.
Carotid Arteries: As the internal carotid arteries travel upward through each hemisphere, they divide into two branches, the anterior and middle cerebral arteries. The anterior cerebral artery supplies the inferior surface of the frontal lobe and the medial parts of the hemisphere. The middle cerebral artery supplies the basal ganglia, deep white matter, and the lateral surface of the hemisphere. The basal ganglia are supplied by small branches of the middle cerebral artery called the lenticulostriatal arteries.
Vertebral/Basilar System: The vertebral arteries run upward through the cervical vertebrae of the neck and enter the skull through the foramen magnum. The two vertebral arteries join and form the basilar artery, which supplies the pons, cerebellum, and midbrain. As the basilar artery reaches the top of the cerebellum, it divides to form two posterior cerebral arteries. These arteries supply the thalamus, medial surface of the temporal lobes, and virtually the entire occipital lobes.
Venous Flow: Blood drains from the brain through shallow and deep systems of venous flow. The surfaces of the hemispheres are drained by superficial veins that flow into the superior sagittal sinus. The inferior surface of the brain and deep structures are drained by a system that eventually forms the straight sinus. The straight and superior sinuses in the posterior part of the brain join to eventually form the jugular veins in the neck.
Stroke (Cerebral Vascular Accident [CVA]): Stroke is a general term used to describe virtually any disturbance in cerebral circulation that results in ischemia and anoxia. Another term commonly employed is cerebral vascular accident (CVA). These disturbances include occlusion of the arteries by fatty emboli or blood clots, breaks in arteries that produce hemorrhage, and ischemia resulting from decreased blood pressure and overall perfusion.
Ischemia: Deficiency of oxygen in a tissue due to obstruction of a blood vessel, causing temporary damage to living cells due to insufficient blood supply.
Atherosclerosis represents the most common mechanism producing focal ischemia. According to the American Heart Association, coronary atherosclerosis is the term for the buildup of fatty substances, cholesterol, cellular waste products, calcium and fibrin (a clotting material in the blood) in the inner lining of an artery. The buildup that results is called plaque. The sclerotic plaque lines the artery walls and builds up over the course of many years. The plaque buildup may eventually reduce arterial flow, completely block the artery, or produce an embolus that flows in the arterial stream to block an artery downstream. Other sources include infection emboli and emboli produced by cardiac disease. Once an artery is occluded, neurons perfused by the artery no longer receive necessary nutrients and oxygen. These cells eventually die, and this results in a focal infarct. The area appears hypodense on neuroimaging, and autopsy reveals a fluid-filled cavity.
Several methods exist for the revascularization of cerebral blood vessels having atherosclerotic lesions. Patients with certain types of coronary insufficiencies documented by certain coronary angiographic findings may be helped symptomatically by coronary artery bypass operations. Other patients sometimes may benefit from other types of arterial surgery, for example, various bypass operations, or endarterectomies, which surgically attempt recanalization of certain occluded blood vessels. These are generally patients with severe disease but yet who meet certain diagnostic criteria and who are healthy enough to undergo what amounts to major surgery with relatively high morbidity and mortality rates. The cost is immense for many of these operations and incumbent hospitalization, including expensive special equipment that is required and special training that is necessary for a team to use the special surgical equipment.
For example, it is estimated that a single coronary bypass operation may cost a patient over $50,000, including hospitalization fees and surgical fees. Availability of this special type of surgery for vascular problems is limited. Long-term efficacy of coronary bypass surgery is as yet unknown, and the appropriate diagnostic and surgical criteria remain controversial.
Attempts have been made to solve the above problems by means of various innovative methods and devices. For example, Russian Patent SU 897251 disclosed in 1982 (inventor I. N. Danilova) describes a method of treating patients suffering from cerebral atherosclerosis with ischemic stroke in the earlier rehabilitation period by introducing 1 to 2% aminalon solution on a daily basis by means of endonasal electrophoresis with gradual increase in the current density from 0.01-0.02 to 0.02-0.03 mA/cm2. The first three to four procedures are carried out for 5 minutes, with 3- to 5-min. intervals between procedures, while duration of subsequent procedures is gradually increased to 15 to 30 minutes. Tests on 53 patients showed that such treatment made it possible to shorten duration of treatment from 1.5 to 3 months to 20 to 25 days.
Russian Patent SU 1722504 disclosed in 1992 (inventor V. I. Fomichov, et al) describes a method for shortening the duration of treating atherosclerosis of coronary blood vessels by means of plasma-absorption introduced in three procedures in an amount of 1000 to 1200 ml during 90 to 120 minutes with 2- to 5-minute intervals between procedures.
German Patent DE 10351949 issued in 2005 to M. Strobl, et al., discloses a method of treating atherosclerosis of coronary blood vessels by using an aneurism stent, e.g., for the widening of intracerebral vessels. The aneurysm stent consists of a container and a stretched structure with a range having changed blood permeability with stretcher structure being tubular and expandable within container which can therefore be partly supported.
U.S. Pat. No. 6,814,962 issued in 2004 to P. Benoit, et al., discloses recombinant viruses and their use in treating atherosclerosis and other forms of coronary artery disease and a method, reagent, and kit for evaluating susceptibility to same. The aforementioned recombinant viruses comprise heterologous DNA sequence coding for a lipase involved in lipoprotein metabolism. The invention also concerns the preparation and use in therapy of said recombinant viruses, especially in the treatment or prevention of dyslipoproteinemia-related pathologies. The method and apparatus of this invention consist of treating gum disease and include a light-producing dental appliance that is accessible exteriorly to the body for placement within the mouth of the patient to expose the mouth to light radiation of a selected wavelength and in an amount that is effective for killing or debilitating pathogenic microorganisms, especially Porphyromona gingivalis within the mouth of the patient such that the bacterial load carried to the heart is diminished, thereby reducing or eliminating the symptoms of coronary artery disease, atherosclerosis vascular inflammation, and plaque formation. The light source may comprise a laser, a source of ultraviolet light such as a low-pressure mercury lamp, a source of visible light such as an incandescent lamp, a flash lamp such as a xenon flash lamp, an arc lamp, a combination mercury-xenon lamp, an Excimer laser, a tunable dye laser, a laser diode, or a light-emitting diode (LED).
U.S. Pat. No. 6,962,585 issued in 2005 to L. Poleo, Jr. describes a catherization system and method for using an artery-blockage-removal system, including a hollow plastic tube with IR optical fibers extending longitudinally between its inner and outer walls. The catherization process includes the following steps: X-Ray dye is injected into an artery to pinpoint the location of a blockage; a guide wire of the catherization system is inserted into the artery to cross the location of the blockage; the catherization system is advanced along the guide wire to abut the blockage; IR and vacuum sources are activated, respectively, to dislodge the blockage from the artery walls and to remove arterial debris without damage to the artery and without risk of debris entering the blood stream.
However, laser treatment becomes especially problematic when it relates to cerebral arteries because intraluminal use of laser radiation, especially in coronary or cerebral blood vessels, is associated with the possibility of perforation of or thermal damage to the vessel walls and surrounding tissue. Accordingly, intravascular recanalization of occluded blood vessels is still an experimental procedure.
Recently, investigators have reported the use of continuous wave (CW) argon, neodymium-YAL, and carbon dioxide laser sources to successfully vaporize, coagulate, and penetrate atherosclerotic plaque in animals and in sections of coronary arteries taken from human cadavers. However, the investigators also report perforation of the vessel walls in many cases, particularly at laser energy levels that have been increased to a level sufficient to effect vaporization of plaque. That may occur because of inaccurate positioning of the end face of the optical fiber from the plaque and because the selected distance is not correlated with laser power.
Such laser energy levels are appropriately characterized as the “thermal” mode of laser operation that involves damage to tissue by virtue of heat accumulation in the tissue impinged by the laser radiation. Excessive heat accumulation causes thermal degradation or thermal necrosis. In other words, the temperature of the tissue rises, tissue proteins are denatured, and ultimately the tissue is coagulated and “evaporated” or “vaporized.” While the laser thermal energy mode is effective in coagulating and vaporizing many tissues, including the tissues forming atherosclerotic plaques and senses, its use by the methods known heretofore in occluded coronary and cerebral blood vessels, for example, is not sufficiently safe and controllable. Consequently, the problem of inadvertent damage to or destruction of surrounding vessel tissue has been a major obstacle in the development of an acceptable microsurgical technique for laser angioplasty in the human vascular system.
U.S. Pat. No. 5,041,108 issued in 1991 to K. Fox, et al., discloses an attempt to solve the problems existing in laser cerebral endovascular treatment by providing a flexible catheter having an outside diameter of approximately 1.2 to 5.0 millimeters, which is especially suitable for use in coronary, cerebral, and somewhat larger carotid blood vessels, for example, to remove occlusions such as athermanous plaques. Within the catheter sheath are optical fibers and fluid channels. In one embodiment, the optical fibers include a bundle of laser-transmitting fibers eccentrically arranged relative to the catheter axis and radially movable toward that axis by means of a balloon positioned within the catheter sheath. Each laser fiber has a distal lens system which converges and cants the radiation beam away from the circumference of the catheter and toward the axis thereof. Alternate embodiments of the catheter include distal lens systems for laser fibers that may comprise one or more diverging lenses for special applications or techniques to be hereinafter described.
Fluid systems within the catheter include an outflow or suction channel for removal of fluids and debris and two or more inflow channels for injection of saline, pharmacologic agents, radio-opaque positioning dyes, immuno-specific antibodies, and the like. Carbon dioxide gas channels are also provided for inflation or deflation of both the laser-aiming balloon and a balloon circumferentially disposed about the catheter adjacent to the distal end thereof for occluding the vascular lumen and for establishing stabilization of the catheter distal end relative to said lumen.
A laser microsurgical system is operatively connected to the proximal end of the flexible angiographic catheter and comprises a proximal optical and fluid coupler for interconnecting the optical fibers and fluid channels of the catheter to the various system components, such as the laser apparatus and control, fiberoptical laser scanner, illumination and visualization systems, positioning systems, and fluid systems. The objects of the aforementioned invention are accomplished according to its method aspects by the use of visible light laser energy in the wavelength range of 351 to 515 nanometers, and, preferably, the blue-green emission lines at wavelengths of 488 and 514 nanometers from an argon-ion laser with a peak power output of about 20 W, such as a Spectra-Physics 171 Laser. The argon laser apparatus is operated in the pulsed or nonconducting mode using a pulse width or duration in the range of 5 to 200 milliseconds and a pulse repetition rate of 1 to 50 pulses per second with a duty cycle between 5 and 50%. The preferred pulse energy is in the range of 150 to 500 millijoules. Spot size for each fiber in the laser fiber bundle may be from 100 to 500 microns, preferably, the largest possible spot size in that range that is compatible with energy density requirements. The above parameters of pulsed laser energy are selected to effect damage to a luminal obstruction with substantially no thermal necrosis of the surrounding tissue.
However, the catheters used for the above methods have a complicated construction and are difficult to operate. Furthermore, they cannot operate with lasers of high power and do not possess sufficient reliability.